Research And Application Of Fiber Gas Sensing Based On Multimode Interference

With the development of industry,all industries will produce toxic and harmful gases,especially petroleum,chemical,coal,and other heavy industries,so the research and development of the detection of these toxic and harmful gases is extremely important.No-core fiber is a kind of multimode fiber with cladding and no core.This new type of structural optical fiber has been studied by many scholars at home and abroad.The basic theory of this paper is the mode interference principle,based on no core optical fiber interference sensor with different sensing structure.Three new composite interferometric measurements of hydrogen sulfide gas sensor structure sensing structures were developed to solve the problem of poor stability and low sensitivity in hydrogen sulfide gas detection in the industrial process by cascaded no-core fiber(NCF)with single-mode fiber(SMF),multi-mode fiber(MMF)and thin-core fiber(TCF).The main researches of this paper are as follows:1.The sensing theory of multi-mode interference type fiber optic sensor is studied for single-mode,no-core and single-mode(SMF-NCF-SMF,SNS)multimode interference type fiber sensor,and it is concluded that the energy distribution and output strength of the optical field in the optical fiber are related to the refractive index of the external environment,the diameter and length of the no-core fiber.The optical simulation software Rsoft is used to simulate the influence of these parameters on the coreless fiber which provides a theoretical basis for the subsequent sensor structure design.2.Nanometer titanium dioxide dispersion was coated on the outer surface of the no-core fiber and fused to both ends of the single-mode fiber to make a no-core-multimode-no-core(NMN)sensor with a sensitivity of 7.36pm/ppm in the range of 0-30 ppm hydrogen sulfide gas concentration.3.The multimode fiber was replaced by single-mode fiber to make the no-cor single-mode-no-core(NSN)sensing element.Titanium dioxide sensitive film was coated on the surface of a coreless fiber,with a sensitivity of 18.93pm/ppm in the range of0-60 ppm hydrogen sulfide gas concentration.4.Titanium dioxide and zinc oxide were compounded,coated on the surface of no-core fiber and fused between two segments of thin core fiber to make a thin core-no-core-thin core(TNT)sensor,with a sensitivity of 21.26pm/ppm in the range of0-50 ppm hydrogen sulfide gas concentration.